The present invention relates to tamper indicating adhesive devices, and more particularly to devices such as tapes, labels, and label stock that indicate tampering attempts through tearing or internal delamination.
It is known to provide a tamper indicating device which may be adhered to various articles. Devices are known that indicate tampering by changing their appearance upon attempts to remove the device from the article.
It may be desirable to place the tamper indicating device on the article to provide some type of information, such a serial number or other identification, or to provide an indication of the authenticity of the article. In such a case, it is desirable to provide an indication of tampering to prevent the device with the information thereon from being removed and re-adhered to another article.
It may be desirable to place the tamper indicating device on an article that is some type of container for the contents inside the article. In such a case, it may be desirable to provide a tamper indicating device across two separable portions of the article. For example, it may be desirable to adhere the tamper indicating device both to the flap and the main body of a carton or envelope. In this way, removal of the tamper indicating device to gain access to the contents will cause the device to provide an indication of tampering.
U.S. Pat. No. 4,876,123, assigned to the assignee of the present application, discloses a light transmissive film derived from a composition comprising 50 to 85 parts by weight of a first copolymer comprising at least one moiety derived from at least one olefinic monomeric unit and 50 to 15 parts by weight of a second copolymer comprising at least one moiety derived from at least one vinyl alcohol monomeric unit and said second copolymer being sufficiently incompatible with said first copolymer such that two phases are formed within said film, one of said phases being continuous. The film can be made into a tape including various colorants and indicia that provide an indication of tampering. When the film delaminates, such as upon attempts to remove it from a container, it becomes opaque so that first indicia are obscured when viewed through the delaminated film, but second indicia become perceptible over the delaminated opaque film. The ""123 patent explains that xe2x80x9cthe film may be produced by any suitable film generating process, but is preferably produced by dry blending the first and second polymers together, air drying the blend at 200xc2x0 F. for 48 hours, then extruding the blend onto a driven chilled roll. Preferably, the film is at least 0.003 inches in thickness. At thicknesses less than 0.003 inches, voids form on the surfaces of the film.xe2x80x9d Column 3, line 63, through column 4, line 2.
U.S. Pat. No. 4,980,222, also assigned to the assignee of the present application, discloses tamper indicating tape based on the same film as that disclosed in the ""123 patent. The devices discloses in the ""222 patent include various arrangements for obscuring and revealing tamper indicating messages, and various ways for adhering the tape to articles.
Although the commercial success of available tamper indicating devices has been impressive, it is desirable to further improve the performance of tamper indicating devices. The present invention provides tamper indicating devices such as tapes, labels, and label stock that comprise a film backing that is thinner and more easily torn or delaminated than the film backing of known devices. Films that tear or internally delaminate more easily are more sensitive and will indicate tampering more readily than thicker, stronger film backings. Surprisingly, such thin film backings can be made by the blown film extrusion process. This process provides thin film that is sensitive to attempts at tampering, yet strong enough to be conveniently and economically handled and converted in products.
One aspect of the present invention provides a tamper indicating device. The device comprises a blown film backing and a layer of adhesive. The backing includes a first, continuous phase and a second, discontinuous phase. The backing is normally light transmissive and becomes opaque upon internal delamination of the backing.
In one preferred embodiment of the above tamper indicating device, the blown film backing contains from 60 to 85 parts by weight of the first, continuous phase and from 15 to 40 parts per weight of the second, discontinuous phase. The first continuous phase preferably comprises a polyolefin. More preferably the first, continuous phase comprises at least 90 parts by weight of a polyolefin having 2 to 4 carbon atoms. The second, discontinuous phase preferably comprises an ethylene/vinyl acetate copolymer or ethylene/vinyl alcohol copolymer. Optionally, the second, discontinuous phase comprises a hydrolyzed ethylene/vinyl acetate copolymer. Alternatively, the second, discontinuous phase comprises an ethylene/vinyl acetate/vinyl alcohol terpolymer, which is preferably essentially completely hydrolyzed,
In another preferred embodiment of the above tamper indicating device, the blown film backing has a draw ratio of at least 10:1. In one aspect of this embodiment, the blown film backing has a blow-up ratio of at least 1.56:1.
In another preferred embodiment of the above tamper indicating device, the blown film backing has a thickness of up to 0.003 inches. More preferably, the blown film backing has a thickness of up to 0.002 inches.
In another preferred embodiment of the above tamper indicating device, the device includes an overlaminate layer on the backing opposite the adhesive.
In another preferred embodiment of the above tamper indicating device, the device includes an initially viewable indicia that becomes obscured upon internal delamination of the blown film backing.
In another preferred embodiment of the above tamper indicating device, the device includes a latent indicia that becomes viewable upon internal delamination of the blown film backing.
In another aspect, the present invention provides an alternative tamper indicating device. The device comprises a blown film backing and a layer of adhesive. The blown film backing comprises: a) 60 to 85 parts by weight of a first, continuous phase comprising a polyolefin; and b) 15 to 40 parts by weight of a second, discontinuous phase comprising an ethylene/vinyl acetate copolymer or ethylene/vinyl alcohol copolymer, or an ethylene/vinyl acetate/vinyl alcohol terpolymer which is preferably essentially completely hydrolyzed. The blown film backing is normally light transmissive and becomes opaque upon internal delamination of the backing.
In one preferred embodiment of the above tamper indicating device, the first, continuous phase comprises at least 90 parts by weight polyolefin having 2 to 4 carbon atoms, and the second, discontinuous phase comprises an ethylene/vinyl acetate/vinyl alcohol terpolymer. Preferably, the blown film backing has a thickness of up to 0.003 inches. More preferably, the blown film backing has a thickness of up to 0.002 inches.
In another preferred embodiment of the above tamper indicating device, the device includes an initially viewable indicia that becomes obscured upon internal delamination of the blown film backing.
In another preferred embodiment of the above tamper indicating device, the device includes a latent indicia that becomes viewable upon internal delamination of the blown film backing.
In yet another aspect, the present invention provides another alternative tamper indicating device. The device comprises a film backing and a layer of adhesive. The film backing has a thickness of up to 0.002 inches. The film backing comprises: a) 60 to 85 parts by weight of a first, continuous phase comprising a polyolefin; and b) 15 to 40 parts by weight of a second, discontinuous phase comprising an ethylene/vinyl acetate copolymer or ethylene/vinyl alcohol copolymer, or an ethylene/vinyl acetate/vinyl alcohol terpolymer which is preferably essentially completely hydrolyzed. The film backing is normally light transmissive and becomes opaque upon internal delamination of the backing.
In a preferred embodiment of the above tamper indicating device, the backing comprises a blown film.
In another preferred embodiment of the above tamper indicating device, the device includes an initially viewable indicia that becomes obscured upon internal delamination of the backing.
In another preferred embodiment of the above tamper indicating device, the device includes a latent indicia that becomes viewable upon internal delamination of the backing.
The present invention also provides an article including any of the tamper indicating devices described herein adhered to the article. The tamper indicating device is adhered to the article by the adhesive with an adhesive bond strength, and the backing has a delamination strength less than the bond strength.
In yet a further aspect, the present invention provides a further alternative tamper indicating device. The device comprises a blown film backing and a layer of adhesive. The blown film backing comprises: a) 60 to 85 parts by weight of a first, continuous phase comprising a polyolefin; and b) 15 to 40 parts by weight of a second, discontinuous phase comprising an ethylene/vinyl acetate copolymer or ethylene/vinyl alcohol copolymer, or an ethylene/vinyl acetate/vinyl alcohol terpolymer which is preferably essentially completely hydrolyzed.
In one preferred embodiment of the above tamper indicating device, the first, continuous phase comprises at least 90 parts by weight polyolefin having 2 to 4 carbon atoms, and the second, discontinuous phase comprises an ethylene/vinyl acetate/vinyl alcohol terpolymer which is preferably essentially completely hydrolyzed.
In another preferred embodiment of the above tamper indicating device, the blown film backing has a thickness of up to 0.003 inches. More preferably, the blown film backing has a thickness of up to 0.002 inches.
The present invention also includes an article having the above tamper indicating device adhered to the article. The device is adhered by the adhesive with an adhesive bond strength, and the device has a tear strength less than the bond strength.
The present invention also includes the blown film backings described herein, along with the methods of manufacture of such film backings and tamper indicating devices.